Psalm 31:21 in the King James Version reads, "Blessed be the Lord: for he hath shewed me his marvellous kindness in a strong city." This verse is part of a longer passage in which the speaker is expressing their trust and gratitude towards the Lord.

The overarching theme of this passage is the idea of finding refuge and strength in the Lord. The speaker is facing difficult circumstances and is seeking solace and protection from God. Throughout the passage, the speaker expresses their confidence in the Lord's ability to deliver them from their troubles and to provide for their needs. Psalm 31:21 specifically highlights the profound gratitude of the speaker, who declares "Blessed be the Lord" for the "marvellous kindness" he has shown in a "strong city."

In this verse, the "strong city" mentioned could symbolize the protection and security that the Lord offers to his followers. The city is often a metaphor for a place of safety and stability, and in this context, it represents the refuge and strength that the speaker finds in the Lord. The "marvellous kindness" that the Lord has shown can be understood as the abundant grace and mercy that he extends to those who trust in him. This kindness is a source of blessing and comfort for the speaker, who acknowledges and celebrates it with gratitude.

The imagery of the "strong city" also suggests the idea of a fortress or stronghold, which are common symbols of God's protection in the Bible. In times of trouble, the Lord is portrayed as a place of refuge and strength, where his people can find security and safety. This imagery conveys the message that the speaker's trust in the Lord is well-placed, as he is a reliable and unwavering source of support.

The overall context of Psalm 31 is one of distress and persecution. The speaker is facing enemies who are seeking to cause them harm, and they are turning to the Lord for deliverance. Throughout the passage, the speaker expresses their anguish and fear, but also their unwavering trust in the Lord's ability to intervene on their behalf. Psalm 31:21 is a culmination of this trust, as the speaker acknowledges the Lord's kindness and protection in the face of adversity.

The themes of trust, gratitude, and divine protection are central to this verse. It serves as a powerful declaration of faith in the midst of hardship, as the speaker acknowledges the Lord's presence and provision in their life. This verse can serve as a source of encouragement and inspiration for believers who are facing their own trials and tribulations, reminding them of the Lord's faithfulness and the strength that can be found in him.

In summary, Psalm 31:21 is a poignant expression of trust and gratitude towards the Lord, who is acknowledged for his marvellous kindness in providing refuge and protection in a strong city. This verse carries themes of divine protection, trust, and gratitude, and serves as a reminder of the strength and security that can be found in the Lord, even in the midst of adversity.